Intrinsic stress in sputter-deposited thin films

Abstract

A review of the sputtered film stress literature shows that the intrinsic stress can be tensile or compressive depending on the energetics of the deposition process. Modeling studies of film growth and extensive experimental evidence show a direct link between the energetics of the deposition process and film microstructure, which in turn determines the nature and magnitude of the stress. The fundamental quantities are the particle flux and energy striking the condensing film, which are a function of many process parameters such as pressure (discharge voltage), target/sputtering gas mass ratio, cathode shape, bias voltage, and substrate orientation. Tensile stress is generally observed in zone 1-type, porous films and is explained in terms of the grain boundary relaxation model, whereas compressive stress, observed in zone T-type, dense films, is interpreted in terms of the atomic peening mechanism. Modeling of the atomic peening mechanism and experimental data indicate that the normalized momentum may be the appropriate stress scaling factor in the compressive stress regime. An idealized stress momentum curve is constructed depicting the three characteristic stress regions. The rapid tensile-to-compressive stress transition often observed in sputtered films may be associated with a threshold phenomenon, occurring at approximately the atomic displacement energy. Furthermore, data indicate that the inverse relationship between intrinsic stress and deposition temperature is a general phenomenon, independent of the nature of the stress, material, or method of deposition.